The present invention relates generally to roofs and, more particularly, to a roof having an improved base sheet.
Although the present invention is applicable to any type of roof, it has particular applicability in connection with its use in built-up and single ply roofs.
Built-up roofs are formed of alternate layers of bituminous material and felt which are assembled or "built-up" in the field. The alternate layers of bituminous material and felt are assembled onto an overlay which overlies an insulation layer. The insulation layer and overlay are attached to a roof deck which typically is made of metal, wood, concrete gypsum or any other conventional deck material.
A typical built-up roof 10, as shown in FIG. 1, may include a corrugated metal deck 11, an insulation layer 12 directly over the deck 10 and an overlay 13 over the insulation layer 12. Typically, the overlay is one-half inch thick fiberboard. Both the insulation layer 12 and the fiber board overlay 13 are fastened to the deck by mechanical fasteners 14, such as screws, which are inserted through a metal plate (not shown). A built-up roof composite 16 is then formed on the base sheet 13. Typically, the built-up roof composite 16 comprises alternate layers of felt and a bituminous material.
The term "built-up roof composite" as used herein means any one of a plurality of different conventional built-up roof composites used on the top of overlays, such as the built-up roof composite described herein, as well as others, such as EPDM, PVC, modified bitumen, coal tar and Hypolon.
The bituminous material is usually of coal tar or asphalt origin and is applied by hot-mopping between alternate layers of the felt.
The primary function of the overlay 13 is to prevent blistering of overlying layers. Additionally, the overlay 13 prevents the bituminous material from dripping into and through the deck 11. Such penetration has a number of disadvantages. First, any dripping during installation can penetrate into the underlying building, thereby causing injury to people and damage to equipment, furnishings, etc. Additionally, dripping, in the case where the underlying deck is made of wood, could also serve to attach the insulation layer 11 to the deck by means of the bituminous material, as well as the mechanical fasteners, thereby making removal of the insulation layer difficult in those situations where it is necessary to replace the roof. Further, the overlay prevents any of the overlying bitumen from passing through the deck and into any interior fire, thereby preventing any further fueling of the fire.
The function of the metal fasteners 14 is to secure the overlay 13 and the insulation layer 12 to the deck 10. Wind storms have caused more damage to roofs than any other nature related incident. Accordingly, the number of fasteners 14 employed must be sufficient to provide sufficient holding power to provide a required amount of wind uplift prevention. In the past, this has resulted in a relatively large amount of closely spaced fasteners being used, adding to the material and labor costs of roof installation.
An alternative structure to the built-up roof is a weather resistant elasto-plastic membrane which may comprise, for example reinforced polyvinyl floride, butyl rubber, vinylidene chlorides and fluorides, polyesters, polyvinyl chloride, neoprene, chlorosulfonated polyethylene, polysulfides, polyurethanes, polyepoxies, acrylates, and other materials having suitable mechanical strength and weather durability. Such structures are generally designated "single-ply roofs" because a single thickness of the weather-resistant membrane is generally sufficient, as compared with the plurality of layers of roofing felt generally required for built-up roofs. In addition to the membrane, a layer of insulating material is also generally provided between the membrane and the roof deck of the structure in single-ply roofs.
The term "roof covering" as used herein means either a built-up roof composite or a single ply membrane.